Event Driven State Machine Lab

BME554L - Fall 2025 - Palmeri

Tip

I would recommend doing this with pencil and paper first, not immediately jumping into a tool. Err on the side of more detail than not.

Digital Kitchen Timer

Generate a state diagram for a simple digital kitchen timer that has the following buttons:

• Start/Stop Button
• Reset Button
• Pause Button
• Up/Down/Left/Right Arrow Buttons (4)

The timer outputs time intervals in the format: HH:MM:SS

Functional States

• The kitchen timer has an “Idle” state when it isn’t actively counting down time. In this state:
  • The Up/Down buttons increment the time for the HH, MM or SS values.
  • The Left/Right buttons let you move between HH, MM and SS.
  • Time intervals will wrap around to 00 when a reasonable max value is exceeded.
  • The Reset button sets all of the time values to 00.
  • The Pause button is inactive.
• Start/Stop will start the timer countdown when in Idle.
• In the Countdown state:
  • The Start/Stop button will stop and reset the countdown interval.
  • The Pause button will pause, but not reset, the countdown time.
• When the countdown is done, the timer enters an Alarm state, where:
  • The Up/Down/Right/Left arrow buttons, Reset and Pause buttons are inactive.
  • Start/Stop will stop the alarm and return the timer to Idle with the previously set countdown time.

Tip

If any functional state expectation isn’t explicitly described above, please implement something reasonable.

Make sure that your state diagram:

• Has initialization (i.e., batteries put in) and termination (i.e., completely powered off) dots.
• Includes all functional states, including (but not limited to):
  • Idle
  • Countdown
  • Paused
  • Alarm
• Consider if states should have entry and exit actions.
• Make sure all transitions between states are annotated with associated triggering events.

Generate the State Diagram

Formally render your state diagram using one of the tools outlined on the State Diagram Tools page.

Gradescope

Upload your rendered state diagram to the associated Gradescope assignment.